Recommendation ITU-R BT.1868
(03/2010)
User requirements for codecs for
transmission of television signals
through contribution, primary
distribution, and SNG networks
BT Series
Broadcasting service
(television)
ii
Rec. ITU-R BT.1868
Foreword
The role of the Radiocommunication Sector is to ensure the rational, equitable, efficient and economical use of the
radio-frequency spectrum by all radiocommunication services, including satellite services, and carry out studies without
limit of frequency range on the basis of which Recommendations are adopted.
The regulatory and policy functions of the Radiocommunication Sector are performed by World and Regional
Radiocommunication Conferences and Radiocommunication Assemblies supported by Study Groups.
Policy on Intellectual Property Right (IPR)
ITU-R policy on IPR is described in the Common Patent Policy for ITU-T/ITU-R/ISO/IEC referenced in Annex 1 of
Resolution ITU-R 1. Forms to be used for the submission of patent statements and licensing declarations by patent
holders are available from http://www.itu.int/ITU-R/go/patents/en where the Guidelines for Implementation of the
Common Patent Policy for ITU-T/ITU-R/ISO/IEC and the ITU-R patent information database can also be found.
Series of ITU-R Recommendations
(Also available online at http://www.itu.int/publ/R-REC/en)
Series
BO
BR
BS
BT
F
M
P
RA
RS
S
SA
SF
SM
SNG
TF
V
Title
Satellite delivery
Recording for production, archival and play-out; film for television
Broadcasting service (sound)
Broadcasting service (television)
Fixed service
Mobile, radiodetermination, amateur and related satellite services
Radiowave propagation
Radio astronomy
Remote sensing systems
Fixed-satellite service
Space applications and meteorology
Frequency sharing and coordination between fixed-satellite and fixed service systems
Spectrum management
Satellite news gathering
Time signals and frequency standards emissions
Vocabulary and related subjects
Note: This ITU-R Recommendation was approved in English under the procedure detailed in Resolution ITU-R 1.
Electronic Publication
Geneva, 2010
 ITU 2010
All rights reserved. No part of this publication may be reproduced, by any means whatsoever, without written permission of ITU.
Rec. ITU-R BT.1868
1
RECOMMENDATION ITU-R BT.1868
User requirements for codecs for transmission of television signals through
contribution, primary distribution, and SNG networks
(2010)
Scope
This Recommendation describes user requirements for the specifications, design, and testing of systems for
the transmission of television signals through contribution, primary distribution and SNG networks.
The ITU Radiocommunication Assembly,
considering
a)
that contribution, primary distribution, and satellite news gathering (SNG) networks are
essential for broadcasting operations and provide a valuable method of transmission for rapidly
acquiring and broadcasting events;
b)
that Report ITU-R BT.2069 − Spectrum usage and operational characteristics of terrestrial
electronic news gathering (ENG), television outside broadcast (TVOB) and electronic field
production (EFP) systems, provides specifications for broadcast auxiliary services (BAS);
c)
that the use of SNG and the technical and operational characteristics for SNG are defined in
Recommendations ITU-R SNG.770, ITU-R SNG.771 and ITU-R SNG.1007;
d)
that the system characteristics of TVOB, ENG and EFP in fixed services and mobile
services are specified in Recommendations ITU-R F.1777 and ITU-R M.1824;
e)
that user requirements for video bit-rate reduction coding of digital TV signals for
an end-to-end television system, with respect to picture formats, coding schemes, and picture
quality have been specified in Recommendation ITU-R BT.1203;
f)
that coding algorithms using bit-rate reduction techniques for television signals have been
devised to enable such transmission to be effective, with the aim of maximizing efficiency and
resources;
g)
that television signals should be transmitted with minimum impairments;
h)
that general advice on methods of assessment and subjective evaluation are defined in
ITU-R Recommendations;
j)
that such assessment will need to take into account the basic picture and sound quality,
failure characteristics when there are errors in the transmission link, and the quality achieved after
downstream processing;
k)
that both the design of codecs and their assessment will need to take into account user
requirements;
l)
that to be complete, the user requirements should specify the test procedures and test
material that should be used to check whether the requirements are being met,
recommends
1
that the following user requirements should be applied for the specifications, design, and
testing of systems for the transmission of television signals through contribution, primary
distribution and SNG networks as part of the broadcasting chain.
2
Rec. ITU-R BT.1868
TABLE 1
Type of transmission network
Input video signal format
Contribution
Primary distribution
SNG/ENG
Sampling: 4:2:2 (Y, CB, CR)
8 or 10 bits per sample for each component
Input audio signal format
Sampling: 48 kHz
20 bits or more
Sampling: 48 kHz
18 bits or more
Sampling: 48 kHz
16 bits or more
Sound channel
Eight channels (typical)
Six channels (typical)
Two channels
(minimum)
Ancillary data
Bit rate: around 100 kbit/s
Maximum relative sound/vision
delay
 2 ms per codec(1)
Basic picture quality (for the
given number of codecs in
tandem in error-free condition)(2)
Three codecs in tandem
Two codecs in tandem
Single codec
Optional requirement for picture
quality (for the given number of
codecs in tandem in error-free
condition)(2)
N/A
Picture quality after colour
matte, after modification to
picture geometry, or after slow
motion(2)
Quality difference:
 18% with DSCQS
method using two
foreground sequences
and appropriate
background material
taken from
Recommendation
ITU-R BT.1210,
between two codecs
Basic sound quality
See Recommendation ITU-R BS.1548, Annex 1
Failure characteristic/error
performance(5)
Quasi-error-free at decoder input for normal condition(3), (4)
Error-concealment functionality should be required for decoders. A signalling
function for errors should be provided
Vision/audio failure
characteristics
Vision failure first
Recovery time(5), (7)
 500 ms after a break of 50 ms(6)
Change in overall delay after
signal interruption/ major
disturbance(5)
Less than 20 s
Quality difference:  12% with DSCQS method using at least four sequences
taken from Recommendation ITU-R BT.1210, at least half of which should be
high-activity sequences. The given quality grade should be met using at least
75% of the sequences chosen; the rest must achieve  20%
N/A
Two codecs in tandem
Quality difference  18%
of the DSCQS or at least
four sequences chosen
from Recommendation
ITU-R BT.1210, at least
half of which should be
high activity sequences.
The given grade should
be met using at least
75% of the sequences
chosen, the rest should
achieve  36%
N/A
N/A
 1 s after a break of
50 ms(6)
Rec. ITU-R BT.1868
3
Notes to Table 1:
DSCQS:
double stimulus continuous quality scale.
DSIS:
double stimulus impairment scale.
N/A:
not applicable.
(1)
The figure of 2 ms per codec was chosen in the light of the maximum discrepancy of 20 ms (sound advanced) or
40 ms (sound delayed) specified in ITU-T Recommendation J.100 for the whole signal chain, taking into account
the likelihood that:
– a number of codecs will be connected in tandem; and
– a major part of the overall discrepancy will occur elsewhere in the signal chain.
(2)
Subjective assessment of picture quality should be carried out in accordance with Recommendations
ITU-R BT.500, ITU-R BT.710 and ITU-R BT.1129.
(3)
Different transmission (modulation) schemes could result in different failure conditions.
(4)
The failure characteristics of digital transmission systems are generally abrupt. It is therefore desirable to provide
a means of switching the form of the transmitted signal to a more robust one in SNG applications and under
conditions likely to jeopardize normal reception. There would therefore be two operation modes. Optimum
methods of doing this need to be investigated. It is anticipated, however, that some reduction in video signal
quality will be incurred when the switch is made; the figure given here indicates what would probably be a
reasonable compromise.
(5)
Further information relating to failure characteristics and recovery time is given in Appendix 1.
(6)
The decoder should maintain a still frame output or a frame of black during resynchronization.
(7)
The recovery time can be measured as the number of fields of delay that is required between the connection of the
signal to the decoder, and switching picture monitor input from a gray-level signal (or a suitably delayed
non-processed signal) to the decoder output signal such that no disruption to picture quality can be observed. A
similar procedure should be adopted to assess the recovery time associated with bit slips, which might occur
following a non-sync cut, for example.
Appendix 1
Further information relating to failure characteristics and recovery time
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Interruptions in any part of the multiplexing lasting several seconds or more are intolerable
and protection modes would be required.
With regard to the response to burst errors of short duration, the synchronizing system
should have adequate protection so that the effect of the errors on the video, audio or data
would not be extended due to the need for resynchronization. By maintaining
synchronization through interruptions, the error-management systems for video, audio and
data could be independent.
It is likely that it will not be possible to protect against interruptions of the order of 50 ms.
After such events, the decoder circuits would have to relock in a manner similar to that of
the initial switch-on. This suggests that the relocking sequence should be completed within
160 ms.
It is important for the overall signal delay through the codec to not change markedly when
influenced by transmission errors or interruptions. The degree to which delays should be
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Rec. ITU-R BT.1868
permitted to change has been suggested by ITU-T Recommendation J.81 where  20 μs
would be a reasonable maximum.
Note that very short duration defects are less tolerable in sound than in the picture.
The degree of protection required for data is heavily dependent on the application. For
example, if the data is being used for system control, this could be very critical and require
powerful protection.
Under normal operating conditions there should be no perceptible effect from channel
errors in video, sound or data.
Switching to the protected link should not cause disruptions in the video, sound, or data
signal and this should be considered in designing systems to protect the performance of
a link in use when it deteriorates.